Automatic exposure refers to that an image capture device automatically adjusts its exposure parameters such as an exposure time, an exposure gain, and an aperture according to different lighting conditions or scenes, so that the brightness of a captured image can achieve expected brightness (e.g., brightness that is neither too dark nor too bright). The automatic exposure in current technology may have adverse effects on the captured image, such as increasing the motion streak (i.e., the apparent streaking of rapidly moving objects in a still image) of the image, or introducing more noise to the image. Therefore, it is desirable to provide methods and systems for automatic exposure to ensure the brightness and the definition of the captured image.